Tri-axial centrifuge apparatus with electrical sensor, acoustic sensor, and x-ray instrument

ABSTRACT

A tri-axial centrifuge apparatus for testing of petro-physical properties of a test sample includes a tri-axial sample holder located within an inner bore of a cell body. An axial pressure fluid supply line delivers an axial pressure fluid to apply an axial pressure on the test sample. A confining pressure fluid supply line delivers a confining pressure fluid to apply a biaxial confining pressure on the test sample. A test fluid holder contains test fluid and is static relative to the cell body. The axial pressure fluid, the confining pressure fluid, and the test fluid are contained in separate flow systems. A centrifuge has a window that is located on a portion of a path of the tri-axial sample holder. The tri-axial sample holder is loaded in the centrifuge and spinning with the centrifuge. An x-ray instrument is static and is aligned with the window of the centrifuge.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation in Part of, and claims priority toand the benefit of co-pending U.S. application Ser. No. 14/514,747,filed Oct. 15, 2014 titled “Tri-Axial Centrifuge Apparatus withElectrical Sensor, Acoustic Sensor, and X-Ray Instrument,” which claimspriority to U.S. Provisional Application No. 61/893,632, filed on Oct.21, 2013, titled “Tri-Axial Centrifuge Apparatus,” the full disclosureof each which is hereby incorporated herein by reference in its entiretyfor all purposes.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

Generally, this disclosure relates to a tri-axial centrifuge apparatusfor testing of petro-physical properties and gathering of geo-mechanicalinformation.

Description of the Related Art

There are a number of limitations related to methods, techniques, andinstruments utilized for reservoir sample testing and analysis. The mostbasic step in any reservoir study is sample preparation. Improper orineffective cleaning practice to bring a sample to a native (original)state can render all efforts of testing and analyses in vain. This stepis the most detrimental to sample analysis, especially in tightunconventional formations, gas shales, and conventional formations ofdual porosities. The various current cleaning process have limitationsof achieving proper capillary pressure to effectively remove impuritiesfrom test samples in order to prepare them for tests and analysis.Attempts to overcome these issues by utilizing harsh processes of heatedsolvents or high flow methods are ineffective. In many instances, suchpractices alter the wettability of test sample, thus defeating theprimary purpose of cleaning the test sample. These artificialalterations in wettability and fluid saturations caused by various knownsample restoration techniques create significant errors inpetro-physical data collected for reservoir evaluation. Inunconventional (gas shale) reservoir analysis, the conventional cleaningprocedures are also largely ineffective because they do not take intoaccount the capillary effect. When the reservoir is formed, hydrocarbonsmigrate into reservoir rock replacing water that was initially present.This is a capillary driven mechanism and there is a need to recreatethis scenario in laboratory studies to mimic the reservoir process.

Once a sample is restored, it can then be subjected to variouspetro-physical tests and analyses. Currently, there are a series oftests performed on different instruments to obtain variouspetro-physical data needed for reservoir characterization and productionanalysis. Typically, several instruments are used to perform electricalproperties analysis to calibrate the electrical log, fluid saturationanalysis, and analysis of Archie's parameters. Another apparatus isneeded to perform capillary pressure above 1000 psi analysis, one toperform fluid wettability analysis, one to perform acoustic velocity fordynamic mechanical properties, and yet another apparatus to performx-ray for saturation distribution. Currently, there is no instrumentthat can perform many of these tests under tri-axial conditions that areobserved in the field.

The need of such an apparatus is immense, especially for evaluation ofunconventional sources, such as tight gas sand, shale, tar sand, andhydrates, as the conventional apparatus in the industry do not performadequate analysis of these formations.

Additionally, existing centrifuge methods are flawed. The sample holdersused in existing centrifuges cannot apply tri-axial stress on thesample, as such samples typically fail at RPM higher than 10,000. Thecapillary pressure such centrifuge devices can attain is notsufficiently high enough to duplicate conditions found in somereservoirs, especially unconventional and depleted reservoirs. With manyof the current centrifuge methods, the measurement for saturation isbased on fluid differentiation and does not incorporate the actualdistribution of fluid in a test sample. Additionally, the test chamberstypically used to hold the test sample cannot handle most of thecorrosive chemicals that are required during the life cycle of sampletests (e.g., solvents, inhibitors, surfactant, enhanced oil recovery(EOR) chemicals and acids). Another concern with current centrifugemethods is that the necessary measurements of rock electrical propertiesare not collected continuously throughout the test. Additionally, theorientation of the test specimen and its distance from the center of thecentrifuge axis, has been problematic with current centrifuge methods.

In every stage of reservoir exploitation, accurate information aboutfluid saturation, pore distribution, capillary pressure, andpermeability is vital. In the exploration stage, such informationprovides estimates for original hydrocarbon in-place and maximum primaryproduction. In later stages of reservoir life cycle, it helps determinevarious secondary and tertiary enhanced oil recovery options,particularly for a most cost effective and profitable scenario. Duringabandonment of the well, the saturation values are imperative to assistin the design of a proper abandonment, such as complete shut off ormaintenance for possible future intervention.

SUMMARY OF THE DISCLOSURE

A tri-axial centrifuge apparatus for testing of petro-physicalproperties of a test sample and gathering of geo-mechanical informationincludes a tri-axial sample holder located within an inner bore of acell body. An axial pressure fluid supply line is operable to deliver anaxial pressure fluid to a fluid chamber of a piston assembly to apply anaxial pressure on the test sample. A confining pressure fluid supplyline is operable to deliver a confining pressure fluid to a cell chamberof the cell body to apply a biaxial confining pressure on the testsample. A test fluid holder contains test fluid. The test fluid holderis sealingly secured to the cell body and static relative to the cellbody. The axial pressure fluid, the confining pressure fluid, and thetest fluid are contained in separate flow systems. A centrifuge has awindow that is located on a portion of a path of the tri-axial sampleholder. The tri-axial sample holder is loaded in the centrifuge andspinning with the centrifuge. An x-ray instrument is static and isaligned with the window of the centrifuge.

In alternate embodiments the tri-axial centrifuge apparatus can furtherinclude a titanium tri-axial test casing, and the tri-axial sampleholder can be located in the tri-axial test casing. The test fluidholder can include glass. The centrifuge can have an at least oneadditional tri-axial sample holder. The centrifuge can include at leasttwo glass windows. The at least one electrical sensor can be operable togather data during the testing of a sample and store data fordownloading at a later time. The at least one acoustic sensor caninclude a transducer. The x-ray instrument can be operable to perform anx-ray scan while the centrifuge is operating. The apparatus can furtherinclude a fluid camera system. The test fluid holder can have anelectrical measurement feed.

In other alternate embodiments, the tri-axial centrifuge apparatus canfurther include an electrical measurement jacket. A piston seal can forma seal between an inner bore of electrical measurement jacket and anouter diameter of a piston member of the assembly. A base seal can forma seal between the inner bore of the electrical measurement jacket and abase member of the tri-axial sample holder. The piston seal and the baseseal can seal the test fluid from the cell body outside of theelectrical measurement jacket.

In yet other alternate embodiments, the tri-axial centrifuge apparatuscan include a tri-axial test casing. The at least one acoustic sensorcan be rotationally fixed relative to the tri-axial test casing. A testfluid circulation system can have a test fluid line extending betweenthe tri-axial sample holder and the test fluid holder and a fluidcirculation line extending outside of the cell body between the testfluid holder and the tri-axial sample holder. The test fluid circulationsystem can provide a fluid circulation path for the test fluid. Thepiston assembly can be an axially oriented piston assembly with a pistonstem located entirely within the inner bore of the cell body. Theaxially oriented piston assembly can be operable to apply the axialpressure on the test sample that is greater than the biaxial confiningpressure applied on the test sample, and be operable to apply the axialpressure on the test sample independent of increasing the biaxialconfining pressure on the test sample.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features, aspects andadvantages of the disclosure, as well as others that will becomeapparent, are attained and can be understood in detail, a moreparticular description of the embodiments of the disclosure brieflysummarized above may be had by reference to the embodiments thereof thatare illustrated in the drawings that form a part of this specification.It is to be noted, however, that the appended drawings illustrate onlycertain embodiments of the disclosure and are, therefore, not to beconsidered limiting of the disclosure's scope, for the disclosure mayadmit to other equally effective embodiments.

FIG. 1 is a schematic perspective view of a tri-axial centrifugeapparatus with the centrifuge lid open, according to an embodiment ofthis disclosure.

FIG. 2 is a schematic sectional view of a tri-axial cell assembly of thetri-axial centrifuge apparatus of FIG. 1.

FIG. 3 is a sectional view of a bottom portion of a tri-axial centrifugeapparatus according to an embodiment of this disclosure.

FIG. 4 is a sectional view of a lid portion of the tri-axial centrifugeapparatus according to an embodiment of this disclosure.

DETAILED DESCRIPTION

Although the following detailed description contains many specificdetails for purposes of illustration, it is understood that one ofordinary skill in the art will appreciate that many examples,variations, and alterations to the following details are within thescope and spirit of the disclosure. Embodiments of the disclosuredescribed herein and provided in the appended figures are set forthwithout any loss of generality, and without imposing limitations, on theclaims.

Looking at FIGS. 1 and 2, the disclosure provides a tri-axial centrifugeapparatus 10 for testing of petro-physical properties and gathering ofgeo-mechanical information. The tri-axial centrifuge apparatus 10includes a tri-axial sample holder 12 and a test fluid holder 14. Thetri-axial centrifuge apparatus 10 also includes a centrifuge 16, atleast one electrical sensor 18, at least one acoustic sensor 20, and anx-ray instrument 22.

In another aspect, the disclosure provides a method of using thetri-axial centrifuge apparatus 10. The method includes obtaining a testsample 24 from a reservoir. In some embodiments, the test sample 24 willbe a reservoir rock with some reservoir fluid within it under ambientconditions of temperature and pressure. In some embodiments, such as alab setting, the test sample 24 can be a frozen rock sample with muchmore reservoir fluids in the rock sample, but still under ambientpressure and lower temperature. The test sample 24 is then loaded in thetri-axial sample holder 12. The tri-axial sample holder 12 is loaded ina tri-axial test casing 26. A tri-axial pressure is applied to thetri-axial test casing 26 and the confining pressure is increased in thetri-axial test casing 26. The pressure, temperature, and fluids areequilibrated for the test sample 24. The test fluid holder 14 isinstalled on the tri-axial test casing 26. A centrifuge test isperformed on the test sample 24. An x-ray scan of the test sample 24 isperformed. Electrical analysis of the test sample 24 is performed.Acoustic analysis of the test sample 24 is also performed.

Embodiments of the present disclosure allow a tri-axial load to beapplied to a test sample 24 to simulate the in-situ conditions of areservoir. Additionally, the high RPM of the centrifuge 16 provides thecapillary pressure similar to that experienced in-situ. In general, theRPM is selected based on how much capillary pressure is required toachieve appropriate test conditions for a selected sample. Forconventional reservoir rock, a capillary pressure of 500 psi (equivalentto about 12,000 RPM) can be sufficient, but for an unconventionalreservoir sample, a capillary pressure of 1500 psi or higher can berequired (equivalent to about 27,000 RPM or higher). Further embodimentsof the disclosure provide a solvent resistant assembly which allows forusage of solvents for stripping hydrocarbons, water, and salt from thesamples. The use of titanium, Teflon®, Torlon®, or glass instead ofconventionally used materials allows for a solvent resistant assembly.The typical solvent mix used in experiments can include toluene,methanol, xylene, chloroform, water, acids, and other industrialhydrocarbon based solvents.

In some embodiments, the tri-axial centrifuge apparatus 10 is capable ofperforming one or more of the centrifuge test, x-ray scan, electricalanalysis, and acoustic analysis simultaneously, thus allowing anefficient and comprehensive test sample study to be performed. An addedadvantage of such testing is that the continuous stressing, distressing,and handling of a test sample 24 for performing each of the testseparately in different instruments, is removed. Additionally,embodiments of the present disclosure allow for integration of thevarious data collected related to various sample properties and allowfor better reservoir modeling. For example, data collected from acoustic(sonic) monitoring during capillary pressure measurements will provideinformation about the mechanical stress changes on the test sample 24,not only as a function of pressure change but also as the formationfluid changes. This information can be used during seismic monitoring ofreservoir production and for tuning simulation for production profiles.In further embodiments, the various tests and analyses are performed insequential steps.

Still looking at FIGS. 1 and 2, the base design of the tri-axialcentrifuge apparatus 10 includes a tri-axial sample holder 12, a testfluid holder 14, a centrifuge 16, at least one electrical sensor 18, atleast one acoustic sensor 20, and an x-ray instrument 22. In otherembodiments, the tri-axial centrifuge apparatus 10 includes a tri-axialcell assembly 28. The tri-axial cell assembly 28 includes a tri-axialtest casing 26, a tri-axial sample holder 12 and a test fluid holder 14.Further embodiments also include at least one of the following: anelectrical measurement jacket 30, electrical measurement feeds 32associated with the test fluid holder 14, and a fluid camera system 34.

Tri-Axial Sample Holder: Turning to FIG. 1, the tri-axial sample holder12 is configured to hold the solid test samples 24 from a reservoir. Thetri-axial sample holder 12 includes a piston assembly 36 and a basemember 38. In general, materials for the piston assembly 36 and basemember 38 should be penetrable to x-rays and have minimal or noelectrical conductance and can be, for example, Torlon® (available fromSolvay Plastics) or glass. Piston assembly 36 includes a piston member40, and a fluid chamber 44. An axial pressure fluid supply line 42supplies axial pressure fluid to fluid chamber 44. A fluid chamber base46 has an opening through which the stem 48 of piston member 40 extends.An end face 50 of piston member 40 engages a first end 52 of test sample24.

Base member 38 has an end face 54 that engages a second end 56 of testsample 24 that is opposite the first end 52 of test sample 24. Testsample 24 is therefore contained between the end face 50 of pistonmember 40 and the end face 54 of base member 38. As axial pressure fluidis added to the fluid chamber 44 by way of axial pressure fluid supplyline 42, the end face 50 of piston member 40 will apply axial force onthe first end 52 of test sample 24, inducing axial stress in test sample24. End face 50 of piston assembly 36 and end face 54 of base member 38can be coated with a substance, such as Teflon®, that will provideelectrical isolation of the test sample 24.

Electrical Measurement Jacket: In certain embodiments, the tri-axialsample holder includes the electrical measurement jacket 30. Theelectrical measurement jacket 30 is a non-permeable, elastomeric, rubberor polyurethane jacket and can be made, for example, of Viton®(available from DuPont). Electrical measurement jacket 30 is a tubularmember that surrounds the test sample 24. A piston seal 58 forms a sealbetween the inner bore of a first end of electrical measurement jacket30 and an outer surface of piston member 40. A base seal 60 forms a sealbetween the inner bore of a second end of the electrical measurementjacket 30 and an outer surface of base member 38.

The electrical measurement jacket 30 is equipped with jacket sensors 62to provide additional measurements of electrical properties of the testsample and saturation distribution data. The electrical measurementjacket 30 is made by incorporating the conductive jacket sensors 62during a vulcanization process of jacket making. The type of jacketsensors 62, number of sensors, and their location is based on samplesize and sample property, such as its mineral composition andhomogeneity. The number of jacket sensors 62 in the electricalmeasurement jacket 30 can be increased and distributed such that variouselectrical measurements are performed on the test sample 24 and thecollected electrical measurement values can provide an electrical image.The data collected by the jacket sensors 62 can be transmitted by way ofleads 64 to a processing unit 66. This type of data gathering can beextremely valuable for heterogeneous samples with layering, unconnectedpore structure, fracture, kerogen concentration, and other sampleanomalies. The data from multiple conductive jacket sensors 62 can beused measure electrical resistance across the test sample 24 and toproduce an image of rock lithology and geology.

Tri-Axial Test Casing: Continuing to look at FIG. 1, the tri-axialsample holder 12 is located within the tri-axial test casing 26.Tri-axial test casing 26 includes a top end cap 68 and a cell body 70.Top end cap 68 has external threads 72 located on an outer surface of areduced diameter portion of top end cap 68. Cell body 70 is a generallycylindrical member with an inner bore 74. Cell body 70 has internalthreads 76 that extend from a cap end of the cell body 70 on an innersurface of inner bore 74 that mate with external threads 72 of top endcap 68. A circumferential casing seal 78 creates a seal between theinner surface of inner bore 74 and the outer surface of the reduceddiameter portion of top end cap 68.

Cell body 70 has a bulkhead 80 proximate to a base end of cell body 70that is opposite the cap end. Bulkhead 80 is a plate that extends fullyacross inner bore 74, so that a cell chamber 82 is defined by bulkhead80, the inner surface of inner bore 74, and top end cap 68. A confiningpressure fluid supply line 84 delivers confining pressure fluid to cellchamber 82 for applying biaxial confining stress on the test sample 24.Bulkhead 80 has an enlarged diameter extending outward to define acircumferential flange 86. Bulkhead 80 is located a distance from thebase end of cell body 70 defining a skirt 88 formed by a portion of cellbody 70 and inner bore 74 that extend past bulkhead 80.

In some embodiments, the tri-axial test casing 26 is made of titanium.Titanium allows for x-ray scanning while the test is in progress. Inother embodiments, the tri-axial test casing 26 is made of Torlon® orglass. In general, materials for the tri-axial cell assembly 28 shouldbe penetrable to x-rays and have minimal or no electrical conductance.In further embodiments, the tri-axial test casing 26 and tri-axialsample holder 12 include both internal and external coatings that areresistant to acids and corrosive chemicals, such as hydrochloric acid,acetic acid, or other acids that would be used to mimic well cleaningand stimulation tests, as well as acids that would be used for chemicalEOR. The tri-axial cell assembly 28 can be loaded in centrifuge 16 andis capable of performing centrifuge saturation and capillary pressuretest at unconfined, hydrostatic, or tri-axial test conditions.

The tri-axial sample holder 12 is equipped with an acoustic sensor 20with p-wave and s-wave components. Acoustic sensor 20 can be a dual modetransducer capable of both sending and receiving information. In someembodiments, the acoustic sensor 20 is located on or in the top end cap68. In some embodiments, the top end cap 68 is isolated from the cellbody 70 of the tri-axial sample holder 12 such that electricalproperties can be measured using electrical sensors 18 in the top endcap 68 and the cell body 70 of the tri-axial sample holder 12 as ground.In such an embodiment, electrical sensors 18 of top end cap 68 canprovide electrical information by way of leads 90 to a processing unit92.

A tri-axial pressure can be applied to test sample 24 within thetri-axial test casing 26. The tri-axial pressure can include the axialpressure, and the confining pressure. In order to apply the axialpressure, axial pressure fluid supply line 42 supplies axial pressurefluid to fluid chamber 44 to apply an axial pressure on test sample 24.

In order to apply the confining pressure a confining pressure fluid isapplied through confining pressure fluid supply line 84 to deliver fluidto cell chamber 82 that surrounds the sides of test sample 24 to apply aconfining pressure or biaxial stress on test sample 24. The axialpressure fluid supply line 42 and the confining pressure fluid supplyline 84 are independent and separate fluid flow paths.

The flow path for the axial pressure fluid is separate and independentfrom the flow path for the confining pressure fluid and separate andindependent from the flow path for test fluid circulation system. Theaxial pressure is applied independent of the confining pressure.Similarly, the confining pressure fluid is separate and independent fromthe flow path for the test fluid circulation system. The axial pressurefluid, the confining pressure fluid, and the test fluid do not mingleand are contained in separate flow systems.

During operation of the tri-axial NMR apparatus 100, the axial pressureis applied and maintained at a magnitude that is higher than theconfining pressure. Having the ability to independently adjust the axialpressure, confining pressure and the capillary pressure allows for thesimulation of the true tri-axial stress conditions that are observed inhydrocarbon reservoirs. The independent axial stress being higher thanthe confining stress is responsible for changes in pore throat structurethat controls fluid mobility in actual subterranean reservoirs. Only byduplicating these conditions can the sample be tested at replicatedownhole pressures.

In the reservoir, rocks and fluid are under tri-axial condition, and fora tri-axial condition to be valid, axial pressure has to be higher thanconfining pressure. In the test apparatus if axial stress is not higherthan confining pressure, the piston member 40 could be pushed out of thetest assembly.

Test Fluid Holder: Continuing to refer to FIG. 2, the tri-axial cellassembly 28 includes a tri-axial test casing 26, a tri-axial sampleholder 12 and a test fluid holder 14. The test fluid holder 14 isconfigured to hold the test fluid. Depending on the test type, the testfluid holder 14 can hold test fluid from the test sample 24, or fluidsto be injected into the test sample 24 such as solvents, acids, orchemicals for EOR.

Test fluid holder 14 includes a fluid sample ring 94 and a fluid samplebase 96. In some embodiments, the fluid sample ring 94 is made of glass.In further embodiments, the fluid sample ring 94 is made of temperaturetreated, industrial grade glass, such as Pyrex® glass. Fluid samplerings 94 of various thicknesses can be used to accommodate variousvolumes of fluids. In general, glass, especially temperature treated,industrial grade glass, can be used because such glass provides clearreadings for capturing various fluid volumes produced. Additionally,glass is neutral with respect to wettability, and it separates air,water, and hydrocarbon fluids quickly. Glass also can be used withalmost all known chemical and corrosive fluids, without negativereaction.

Fluid sample base 96 is a generally cylindrical member and can be formedof metallic or non-metallic materials. Fluid sample ring 94 extends fromskirt 88 of cell body 70 to a reduced diameter portion of fluid samplebase 96. A first fluid sample seal 98 creates a seal between an innersurface of the fluid sample ring 94 and an outer surface of skirt 88. Asecond fluid sample seal 100 creates a seal between an inner surface ofthe fluid sample ring 94 and an outer surface of the reduced diameterportion of fluid sample base 96. Double ended screws 102 releasably joincircumferential flange 86 of cell body 70 to an enlarged diameterportion of fluid sample base 96. By joining fluid sample base 96 to cellbody 70, fluid sample ring 94 is maintained in position relative totri-axial test casing 26. A fluid reservoir 104 is defined by the innerbore of fluid sample ring 94, a face of bulkhead 80 and a surface offluid sample base 96.

Test Fluid Circulation System. A test fluid line 105 carries test fluidfrom the tri-axial sample holder 12 to the fluid reservoir 104. A firstfluid circulation line 106 carries test fluid between the fluidreservoir 104 and an isolation valve 108. A second fluid circulationline 110 carries test fluid between the isolation valve 108 and thetri-axial sample holder 12. Isolation valve 108 can be used during thesetup of the test to manage the fluids and can provide a connectionpoint between the first and second fluid circulation lines 106, 110.

Test fluid line 105, first fluid circulation line 106, and second fluidcirculation line 110 together form test fluid circulation system 109.Test fluid circulation system 109 provides a continuous circulation oftest fluid between fluid reservoir 104 and tri-axial sample holder 12.During the loading of the test sample when axial and confining pressuresare applied on the test sample 24, test fluid line 105 that is connectedto bottom plate 54 keeps the sample under a drain condition. As used inthis disclosure, a drain condition means that as the axial and confiningpressure are raised on the sample, the fluid within test sample 24squeezes out through test fluid line 105 and no capillary or internalfluid pressure is formed. Any fluid inside test sample 24 remains underambient pressure condition.

Capillary pressure is generated in test sample 24 once the tri-axialcore holder with sample 24 under tri-axial stress condition, startsspinning in the centrifuge. As the centrifuge spins, a centrifugal forceis applied on the fluid inside test sample 24, which creates capillarypressure within the sample 24. The capillary pressure is generated onlywhen sample 24 is spinning in the centrifuge.

The importance of obtaining capillary pressure values when test sample24 is spinning in the centrifuge under tri-axial condition is that rockin a reservoir is subject to tri-axial conditions and are not inhydrostatic conditions. In hydrostatic conditions the axial stress isgenerally equal to the confining stress. Capillary pressure is functionof pore size and pore throat, both of which have different valuesdepending what kind of stress is applied on the rock, hydrostatic ortri-axial.

In further embodiments, the tri-axial centrifuge apparatus 10 includeselectrical measurement feeds 32 associated with the test fluid holder14. The test fluid holder 14 is designed such that the fluid sample base96 is made of material that is electrically insulated and is embeddedwith electrodes 12 for performing 2 or 4 electrode conductivity andresistivity measurements. The electrical measurement feeds 32 areconnected to electrodes 112 of the test fluid holder 14 to deliversignals to a processing unit 114 for data collection regarding reservoirsalinity information from native state samples which will allow forbetter reserve estimation. In certain embodiments, the electricalmeasurement feeds 32 can provide current and measure the voltage with asmall battery operated device (not shown) that can be installed on therotor 116 of centrifuge 16 (FIG. 1) and connected to the tri-axial cellassembly 28.

Centrifuge: Returning to FIG. 1, any centrifuge 16 that can work withinthe provided test parameters will be acceptable for use in embodimentsof this disclosure. In some embodiments, a centrifuge such as theHettich centrifuge Roto-Salina, which is outfitted for a higher RPM(20,000 rpm and higher) can be used. Such centrifuges have tubs 118 withlarger diameters which provide a higher capillary pressure at a givenRPM as compared to industry standard centrifuges. In the embodiment ofFIG. 1, the rotor 116 of the centrifuge 16 is shown with 4 tri-axialcell assemblies 28. In some embodiments, the rotor 116 of the centrifuge16 is designed to hold 1, 2, 3, or 6 tri-axial cell assemblies 28. Thenumber of tri-axial cell assemblies 28 that can be placed in the rotor116 will be based on specific test parameters.

Centrifuge 16 has a window that is located on a portion of a path of thetri-axial sample holder 12. In some embodiments, the bowl or tub 118 ofthe centrifuge 16 has at least two glass tub windows 120, 122 for x-rayscanning and the fluid camera system 34, respectively. In furtherembodiments, the top or lid 124 of the centrifuge 16 has two lid windows126, 128 aligned with the tub windows 120, 122 for x-ray scanning andthe fluid camera system 34, respectively. In further embodiments, thetub 118 and the lid 124 each have a single window that can be used forboth x-ray scanning and the fluid camera system 34. In yet furtherembodiments, as shown in FIGS. 3-4, the tub 118 has a single tub window130 for x-ray source 133 (FIG. 1) and the lid 124 has a first lid window132 opposite the single tub window 130 for x-ray camera 134 (FIG. 1). Insuch an embodiment, lid 124 has a second lid window 136 for a visualcamera light source 138 (FIG. 1) and a third lid window 140 for visualcamera 142 (FIG. 1).

Electrical sensors: Returning to FIG. 1, a variety of electricalmeasurements can be taken during testing. For instance, in someembodiments electrical analysis of the test sample 24 includes measuringat least one of the resistance, conductivity, capacitance, or impedanceof the test sample. In some embodiments, electrical analysis of the testsample 24 includes measuring at least one of electrical conductance,resistance, or impedance as a function of variable frequency of inputcurrent. In some embodiments, the top end cap 68 of the tri-axial testcasing 26 is designed such that it is isolated from the rest of thetri-axial test casing 26 and acts as an electrode. The cell body 70 ofthe tri-axial test casing 26 can be used as a ground to measure theelectrical properties of the test sample 24 during a test. Electricalmeasurements can be taken at least one of two ways during a test. In thefirst, the centrifuge 16 is stopped at each capillary pressureequilibrium step, taking the tri-axial test casing 26 out, and measuringthe electrical properties. Depending on the test design, additionalequilibrium steps can be required. In some embodiments, there can be 2to 15 equilibrium steps and measurements can be performed at each step.In a second method, processing unit 92 is a battery operated electricalmeasurement device with capability to gather the time domain data thatcan be down loaded at the end of test. The advantage of the secondmethod is that it provides a continuous measurement without a need ofstopping centrifuge 16 and also provides transit data between thecapillary pressure equilibrium stages. Thus, an embodiment of thepresent disclosure includes a processing unit 92 that is operable togather data during the testing of a sample and store data fordownloading at a later time. In further embodiments, the data isdownloaded in real time. In further embodiments, the electrical datacollected on the test sample 24 can be collected simultaneously as theother data is collected, or in sequential steps to the other data. Infurther embodiments, an electrical sensor 18 measures the electricalproperties of fluid contacting the surface of the tri-axial test casing26.

Acoustic sensors: A variety of acoustic measurements can be taken duringtesting, including sonic velocity data. In some embodiments, theacoustic sensor 20 can collect longitudinal wave, shear wave, andStonely wave data. The acoustic data collected can be delivered toprocessing unit 144 by way of leads 146 and analyzed for both time andfrequency domain. The same acoustic sensor 20 can collect the variouswave forms, as one transducer can encompass crystals for longitudinaland shear wave. In certain embodiments, the acoustic sensor 20 is atransducer with both longitudinal wave and shear wave components whichare installed on the top end cap 68 of the tri-axial test casing 26. Insome embodiments, the acoustic sensor 20 is a dual mode transducer andworks in reflective mode to transmit and receive acoustic wave. In someembodiments, the tri-axial centrifuge apparatus 10 is operable tomeasure the acoustic velocity of the test sample 24, as well as thevelocities of the various fluids in the test fluid holder 14. The sameacoustic sensor 20 can perform all of the desired the measurements withproper calibration of the acoustic sensor 20 before the test starts andonce the test is concluded, dependent on rock sample properties andfluid used during the test. The acoustic velocity of the fluid in thetest fluid holder 14 can be used to analyze production and presence ofsolid particles such as grain, asphaltene, and so forth. In general,special care should be taken to assure that the acoustic sensor 20 andassociated components does not interfere with electrical measurements.The acoustic data collected on the test sample 24 can be collectedsimultaneously with the other data, or in sequential steps to the otherdata.

X-Ray: X-ray instrument 22 can be any x-ray that allows for scanning ofa moving object. For example, Hamamatsu manufactures such devices. Thex-ray instrument 22 shown in FIG. 1 includes an x-ray source 133 and anx-ray camera 134. In the embodiment of FIGS. 1 and 3-4, the x-ray source133 is located below the centrifuge tub 118 while the x-ray camera(image capture system) 134 is installed on the lid 124 of the centrifuge16. The x-ray instrument 22 is static and is aligned with a window ofthe centrifuge 16.

The x-ray instrument 22 is capable of performing a whole sample scanwhich provides accurate saturation profiles of various fluids in thetest sample 24 at each equilibrium stage while the centrifuge 16 isspinning. However, there is a RPM limitation on the x-ray instrument 22,so a different technique is utilized at higher RPM. For instance, athigher RPM, such as about 10,000 and above, once the equilibrium forfluids is achieved, the RPM can be reduced to a lower RPM, such as 2,000RPM for sample scanning, and then the RPM can be raised back to theoriginal higher RPM of about 10,000 and above. This does not affect thesaturation distribution as equilibrium is already achieved beforelowering the RPM. In certain embodiments, the x-ray instrument 22 canallow for computed tomography (CT) imaging.

Fluid Camera System: Looking at FIG. 1, in further embodiments, thetri-axial centrifuge apparatus 10 includes a visual fluid camera system.The fluid camera system 34 includes visual camera light source 138 and avisual camera 142. Visual camera light source 138 can be a strobe lightsource and visual camera 142 can be a high speed camera to captureimages as the test progress. The image capturing and fluid levelanalysis is greatly aided by use of glass throughout the tri-axialcentrifuge apparatus 10, which provides for clear images and sharpcontrast between various fluids. The fluid camera system 34 is designedto work both in transmission and reflection mode, i.e., the visualcamera light source 138 and visual camera 142 can be installed on theopposite side of the test sample 24 (e.g., top and bottom) or on thesame side (e.g., top) and use a reflective mirror setup in the tub 118to capture images. The mirror setup can be utilized in cases of limitedaccess on the tub. In the embodiment of FIG. 1, the visual camera lightsource 138 is installed above the lid 124 of the centrifuge 16 andvisual camera 142 is installed below the centrifuge tub 118. In theembodiment of FIGS. 3-4, both the visual camera light source 138 andvisual camera 142 are installed above the lid 124 of centrifuge 16. Useof such a fluid camera system 34 allows for reading of fluid volumes asthey are produced.

Temperature Sensor: The temperature sensors 148 used in embodiments ofthe disclosure include typical infrared high precision temperatureprobes that are available off the shelf. For example, such temperaturesensors are available from Raytek. Temperature sensors 148 can bepositioned in multiple locations on or around tri-axial centrifugeapparatus 10.

Centrifuge capillary pressure under tri-axial, confining, and unconfinedstress conditions can be performed with the tri-axial centrifugeapparatus 10. In some embodiments, capillary pressure over 20,000 psifor an oil/gas/water system can be analyzed. The range of capillarypressures to be tested will depends on the type of reservoir. Forexample, for unconsolidated sand reservoirs, capillary pressures canrange from 0.1 psi to 100 psi; for conventional reservoirs capillarypressures can range from 1 psi to 200 psi; for unconventional reservoirslike shale and tight gas sand (TGS), capillary pressures can range from100-100,000 psi. It should be noted that in instances with a capillarypressure of above 30,000 psi, sample integrity can be an issue. In manysuch cases, a work around can be developed by increasing the tri-axialstress. The test can be conducted as air/water, air/oil, water/oil andin limited cases all three phases (air/oil/water) on the rock sample.Thus, embodiments of the present disclosure allow for extracting ofreservoir core samples with hydrocarbon solvents at capillary pressureof 20,000 psi and higher. In some embodiments, capillary pressure above20,000 psi is achieved by expanding motor speed (RPM), increasing thesize of tub 118, increasing the distance between the test sample 24 andcenter of centrifuge 16, and changing sample size and orientation. Insome embodiments, the test sample 24 is loaded in the centrifuge 16 in avertical orientation. In other embodiments, the test sample 24 is loadedin the centrifuge 16 in a horizontal orientation. In some embodiments,the test sample 24 can be about 0.5 inches to about 8 inches in diameterand about 0.5 inches to about 12 inches in length or smaller.

The large range of data collected (acoustic, temperature, electrical,x-ray, saturation, fluid volumes, rate of fluid volumes, and saturationchange) provides a more complete picture of test progression that can beintegrated with log and seismic data for monitoring and evaluatingeffectiveness of field treatment. Temperature can be monitored using thetemperature sensors 148, rate of fluid volumes can be monitored usingthe fluid camera system 34, and saturation changes can be monitored withthe x-ray instrument 22. For example, electrical data can be generatedfor the wells where logs are not available or are not representativewith a combination of seismic, acoustic, electrical and saturation data,along with well test information.

Test sample preparation: In some embodiments, the disclosure providesthe ability to use solvents to establish the test sample's 24 saturationand to bring test sample 24 to a virgin clean state. Given that thetri-axial centrifuge apparatus 10 and its components are made of solventresistant material, the tri-axial centrifuge apparatus 10 allows forsample cleaning within centrifuge 16 setup. The procedure will varybased on solvents to be used. A given test sample 24 can be cleaned withmultiple solvents. In some embodiments, for each solvent, the tri-axialcell assembly 28 will be removed from centrifuge 16 and the test fluidholder 14 will be filled with the desired solvent. The test sample 24will then be centrifuged with that solvent. This step can be repeateduntil all desired solvents have been used. In further embodiments, eachcleaning step can involve the use of more than one solvent.

A test procedure according to an embodiment of the disclosure isprovided according to the following steps. A test sample 24 is obtainedfrom a reservoir. The tri-axial centrifuge apparatus 10 and test sample24 are prepared based on test sample 24 condition and test requirements.The test sample 24 is loaded in the tri-axial sample holder 12 andplaced in an electrical measurement jacket 30. The assembled jacketedtri-axial sample holder 12 is loaded in the cell body 70 of tri-axialtest casing 26 and the top end cap 68 is screwed on, making sure thetest fluid line 105 from the jacketed tri-axial sample holder 12 isextending out of the bulkhead 80 of the tri-axial test casing 26. As thetop end cap 68 is tightened, the rotation of the test fluid line 105 ismonitored for twisting. As the top end cap 68 is tightened, the testfluid line 105 should not twist. The axial stress on the test sample 24is slowly increased by injecting axial pressure fluid through axialpressure fluid supply line 42 and into fluid chamber 44, and the testfluid line 105 is monitored. The pressure is raised between 100-200 psi.The confining pressure is increased by injecting a confining pressurefluid, such as mineral oil, through confining pressure fluid supply line84 and into cell chamber 82 of the tri-axial test casing 26. Confiningpressure can also be monitored using colored water so as to identify anyleak occurring during the test. In instances where water is used, thewater must first be degassed. Care should be taken to ensure that theaxial stress remains above the confining stress. The test fluid line 105can continue to be monitored to ensure that it remains in place. All thesample pressures, fluids, and temperature can then be equilibrated todesired test conditions.

The test fluid holder 14 is then installed on the tri-axial test casing26, the combination defining the tri-axial cell assembly 28. A dataacquisition capsule, which can include one or more of processing units66, 92, 114, and 144 can be added to the tri-axial cell assembly 28 andthe tri-axial cell assembly 28, including the test sample 24, can beloaded in the centrifuge 16. Temperature, pressures, and fluids areequilibrated to desired test conditions. This second equilibrium step isrelated to usual movement (wobble) that is present in centrifuges at lowRPM, and this must be monitored and equilibrated such that the fluidlevels in the tri-axial cell assembly 28 are stable. The visual, x-ray,acoustic, and electrical data acquisition systems are started then thecentrifuge test is started.

Embodiments of the present disclosure provide for data relating tosaturation, capillary pressure, electrical properties, and permeability.Additionally, the range of temperatures, pressures, and fluids that canbe used during the testing and analysis with this described apparatus isnot available in the industry at this point. Embodiments of the presentdisclosure allow for testing of temperature, pressures, and fluids thatmimic reservoir conditions. Thus, the testing parameters are dependenton reservoir condition and type of studies to be conducted.

The tri-axial stress test conditions, in combination with highercapillary pressure conditions, make it possible to test unconsolidatedsand such as Alberta heavy oil tar sand, and perform various fluidinjection regimes to extract heavy oil in a much shorter timeframe thandone with conventional core flow setup based on flow rate. Also, theconventional core flow method is extremely dependent on the flow channeland therefore it is almost impossible to achieve any appreciablecapillary pressure study permeability or saturation.

The tri-axial stress test conditions, along with higher capillarypressure conditions, x-ray saturation monitoring, fluid volume change inthe test fluid holder 14 as a function of time, and capillary pressure,provide for testing for shale (oil/gas). With conventional flow methods,the injection fluids cannot achieve the required high capillary pressureas the fluids find a channel to flow through and the rest of the testsample 24 does not experience the capillary pressure. In unstressedcentrifugation, the sample has a much higher chance of failure. Theadded caveat in working with shale is its heterogeneity in matrix,layering and presence of kerogen. Due to these issues, historicalanalysis has relied on a crush test which delivers unreliable resultsfor saturation, capillary pressure, and matrix permeability.

The tri-axial centrifuge apparatus 10 with its various data acquisitionand high capillary pressure provides an avenue to perform fracture testanalysis needed for hydraulic fracturing, especially in tight gas sandand shale. Given that shale is ductile, a tri-axial analysis providesthe strength needed to keep the test sample intact. Tests on fracturedcores with or without propant embedment provides differentiation of flowthrough the matrix versus fracture. This cannot be achieved with aconventional core flow test conducted in the industry, especially onun-conventional rock samples.

In further embodiments of the disclosure, a modified version of theapparatus will be operable at a well site with drill cuttings and mudand other fluid analysis.

In further embodiments, integration of test data and measurementsrelating to sonic, resistivity (induction log), gamma and porosity(neutron logs) can be extended to wells where cores were not taken.Thus, extrapolation of data can allow for greater understanding ofunsampled regions.

In yet further embodiments, the disclosure provides for fluid analysisunder reservoir conditions to better understand phase behavior as afunction of capillary pressure change, segregation of different densityfluids, and separation of solids and their effects on sonic velocities.Additionally, fluid analysis related to formation damage and flowassurance can be performed. Analysis for formation damage is the samesetup as described as for other analysis. Since the components of thetri-axial centrifuge apparatus 10 are made of materials that areresistant to chemical damage, the various chemicals that cause formationdamage can be used with the tri-axial centrifuge apparatus 10. For flowassurance, the effect of segregation of solids (asphaltene, wax, etc.)can be quantified during a phase behavior tests. The phase behavior teston reservoir fluids can also be conducted by filling the chamber withreservoir fluid under reservoir condition and centrifuging to separatevarious phases based on density using centrifugation gravitationalforces. The acoustic sensor 20 and x-ray instrument 22 will assist insegregating various phases.

The tri-axial nature of the tri-axial centrifuge apparatus 10 providesthe strength needed to increase the capillary pressure on the testsample 24 to a much higher pressure than currently possible in existingcentrifuges. The combination of the various data collected (x-ray,resistivity, acoustic, visual, etc.) provides a much neededcomprehensive test instrument. The tri-axial centrifuge apparatus 10also can increase data accuracy and efficiency of data delivery. Thetri-axial centrifuge apparatus 10 also can provide cost savings as itallows for running tests simultaneously and provides more accuratereserve estimation, production profiles, and improves EOR planning.

In general, embodiments of the present disclosure improve the existingmethod of core and fluid testing, allow better control on data; improvetest quality; reduce time for certain time critical data collection andanalysis; provide a means of analyzing unconventional reservoirs suchas, tight gas sand, shale (oil/gas), hydrate, tar sand, heavy oil, andlow saturation reservoirs; provide a single source test apparatus toprovide petrophysical data calibrated to electrical logs for saturation;provide a single source test apparatus for calibration of acoustic andseismic logs; provide a single source test apparatus for analysis oftri-axial stresses on petrophysical properties such as wettability,capillary pressure, permeability and saturation of various fluids; andprovide a tri-axial centrifuge apparatus that works well both in alaboratory setting or in the field.

Although embodiments of the present disclosure have been described indetail, it should be understood that various changes, substitutions, andalterations can be made hereupon without departing from the principleand scope of the disclosure. Accordingly, the scope of the presentdisclosure should be determined by the following claims and theirappropriate legal equivalents.

The singular forms “a,” “an” and “the” include plural references, unlessthe context clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value, toabout another particular value. When such a range is expressed, it is tobe understood that another embodiment is from the one particular valueto the other particular value, along with all combinations within saidrange.

As used herein and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

What is claimed is:
 1. A tri-axial centrifuge apparatus for testing ofpetro-physical properties of a test sample and gathering ofgeo-mechanical information, the tri-axial centrifuge apparatus having: atri-axial sample holder located within an inner bore of a cell body; anaxial pressure fluid supply line operable to deliver an axial pressurefluid to a fluid chamber of a piston assembly to apply an axial pressureon the test sample; a confining pressure fluid supply line operable todeliver a confining pressure fluid to a cell chamber of the cell body toapply a biaxial confining pressure on the test sample; a test fluidholder containing test fluid, the test fluid holder being sealinglysecured to the cell body and static relative to the cell body, where theaxial pressure fluid, the confining pressure fluid, and the test fluidare contained in separate flow systems; a centrifuge with a window thatis located on a portion of a path of the tri-axial sample holder, wherethe tri-axial sample holder is loaded in the centrifuge and spinningwith the centrifuge; an x-ray instrument, where the x-ray instrument isstatic and is aligned with the window of the centrifuge.
 2. Thetri-axial centrifuge apparatus of claim 1, further including a titaniumtri-axial test casing, and wherein the tri-axial sample holder islocated in the tri-axial test casing.
 3. The tri-axial centrifugeapparatus of claim 1, wherein the test fluid holder includes glass. 4.The tri-axial centrifuge apparatus of claim 1, wherein the centrifugeincludes an at least one additional tri-axial sample holder.
 5. Thetri-axial centrifuge apparatus of claim 1, wherein the centrifugeincludes at least two glass windows.
 6. The tri-axial centrifugeapparatus of claim 1, wherein the at least one electrical sensor isoperable to gather data during the testing of a sample and store datafor downloading at a later time.
 7. The tri-axial centrifuge apparatusof claim 1, wherein the at least one acoustic sensor includes atransducer.
 8. The tri-axial centrifuge apparatus of claim 1, whereinthe x-ray instrument is operable to perform an x-ray scan while thecentrifuge is operating.
 9. The tri-axial centrifuge apparatus of claim1, further including a fluid camera system.
 10. The tri-axial centrifugeapparatus of claim 1, wherein the test fluid holder has an electricalmeasurement feed.
 11. The tri-axial centrifuge apparatus of claim 1,further including an electrical measurement jacket.
 12. The tri-axialcentrifuge apparatus of claim 11, further including a piston sealforming a seal between an inner bore of electrical measurement jacketand an outer diameter of a piston member of the assembly, and a baseseal forming a seal between the inner bore of the electrical measurementjacket and a base member of the tri-axial sample holder, the piston sealand the base seal sealing the test fluid from the cell body outside ofthe electrical measurement jacket.
 13. The tri-axial centrifugeapparatus of claim 1, further including a tri-axial test casing, andwherein the at least one acoustic sensor is rotationally fixed relativeto the tri-axial test casing.
 14. The tri-axial centrifuge apparatus ofclaim 1, further including a test fluid circulation system having a testfluid line extending between the tri-axial sample holder and the testfluid holder and a fluid circulation line extending outside of the cellbody between the test fluid holder and the tri-axial sample holder, thetest fluid circulation system providing a fluid circulation path for thetest fluid.
 15. The tri-axial centrifuge apparatus of claim 1, where thepiston assembly is an axially oriented piston assembly with a pistonstem located entirely within the inner bore of the cell body.
 16. Thetri-axial centrifuge apparatus of claim 15, where the axially orientedpiston assembly is operable to apply the axial pressure on the testsample that is greater than the biaxial confining pressure applied onthe test sample, and is operable to apply the axial pressure on the testsample independent of increasing the biaxial confining pressure on thetest sample.